This invention relates generally to nuclear reactors, and more particularly to nuclear fuel rods for water-moderated commercial reactors.
Current practice in water reactors is to use fuel rods having Zircaloy cladding encapsulating a column of uranium dioxide (UO.sub.2) pellets in fuel assemblies where the fuel rods are spaced apart and supported by a plurality of grids. Typically, several of these grids are positioned axially along the full length of the fuel rods, which is typically 10 to 15 feet. The conventional UO.sub.2 pellet is a solid cylinder with a variety of end shapes, usually dished and chamfered.
Recently, commercial nuclear power plant owners have found it advantageous to burn the nuclear fuel in longer cycles to improve the economics in view of the inability to reprocess spent fuel. One fuel pellet design which is known to permit extended burnup is in the form of a hollow cylinder. When stacked in columns of the type required for commercial water reactors, these hollow pellets form a long and continuous central passage within the fuel rod. During operation, the fuel pellets can crack, forming pellet debris which can enter the passageway and accumulate at the bottom of the fuel rod. If this debris deposit is sufficiently large, the redistribution of the UO.sub.2 in the fuel rod could significantly affect the power distribution generated by the fuel rod. This redistribution is not desirable and may in some instances limit the operating level of the reactor.